With downsizing and weight reduction of electronic devices such as a mobile phone and personal computer proceeding in recent years, devices with its movable housing openably and closably attached to its stationary housing, so-called a folding type, have been increasing. Accordingly, in folding mechanism used for these devices, reliable opening/closing operation and ease of use are demanded.
A description will be made for such a conventional folding mechanism, using FIGS. 4 and 5. FIG. 5 is an exploded perspective view of the conventional folding mechanism. As shown in the figure, stationary part 1A is formed on the left side of stationary body 1 substantially tubelike. Stationary body 1 is fastened onto the left end of stationary shaft 2 substantially column-shaped, and at the same time, stationary shaft 2 projects to the right from the center of the right side of stationary body 1.
Further, stationary body 1 is integrally fastened to stationary case 3 with stationary part 1A projected from the left side of stationary case 3 substantially tubelike, and also notch 3A is provided at the left end of stationary case 3.
Meanwhile, movable body 4 substantially ring-shaped is polygonal. Movable case 5 is substantially tubelike. Movable body 4 is integrally fastened onto the right inner surface of movable case 5, and also they are arranged rotatably in the open/close direction as against stationary body 1.
Additionally, coiled spring 6 is arranged in a slightly twisted state between the right side of stationary body 1 and the left side of movable body 4. Projection 6A at the left end and projection 6B at the right end are locked to notch 3A of stationary case 3 and notch 4A of movable body 4, respectively. In this way, movable body 4 is biased in the open direction as against stationary body 1, namely counterclockwise, by means of spring 6.
The right end of stationary shaft 2 is inserted into the hollow of movable body 4 and spring 6, and is rotatably attached on the right side of movable case 5 by means of retaining ring 7. Stationary part 1A of stationary body 1 rotatably projects from the left side of movable case 5. Stationary body 1, movable body 4, spring 6, and others are contained in movable case 5 to compose folding mechanism 10.
Folding mechanism 10 composed in this way is used for an electronic device such as a mobile phone shown in FIG. 4B. Stationary part 1A of stationary body 1 is fastened to stationary housing 22 formed on its top surface with operation unit 22A having a plurality of keys and audio input unit 22B such as a microphone. Further, the outer circumference of polygonal part 5A at the right end of movable case 5 is fastened to movable housing 23 formed on its surface with display unit 23A such as an LCD and audio output unit 23B such as a speaker. In this way, a mobile phone is composed with movable housing 23 pivotally supported openably and closably as against stationary housing 22 by means of folding mechanism 10.
In the above-mentioned makeup, in a state of movable housing 23 as shown in FIG. 4A closed, movable body 4 is biased in the open direction as against stationary body 1, namely counterclockwise, because spring 6 of folding mechanism 10 is in the most twisted state. Meanwhile, movable housing 23 is locked to stationary housing 22 by means of a key-like ratchet (not illustrated) provided between stationary housing 22 and movable housing 23, and thus movable housing 23 is retained in a closed state. When push button 24 on the side of stationary housing 22 is pressed in this closed state, the ratchet is released to bias movable body 4 in the open direction, namely counterclockwise, by means of spring 6. Accordingly, a force to open is applied to movable housing 23 as shown by the arrow in FIG. 4B.
After then, as shown in FIG. 4C, when movable housing 23 opens at a given angle of around 150 to 170 degrees as against stationary housing 22, a force in the open direction of folding mechanism 10 is stopped by means of a stopper mechanism (not illustrated) separately provided between stationary housing 22 and movable housing 23. Consequently, a state of movable housing 23 open at a given angle is retained.
That is to say, as a result that push button 24 is pressed, movable body 4 fastened to movable housing 23 through movable case 5 and biased by spring 6 in the open direction is rotated to open and close movable housing 23 as against stationary housing 22.
An electronic device having such a makeup is disclosed in Japanese Patent Unexamined Publication No. 2002-335316.
However, in the conventional folding mechanism mentioned above, when pressing push button 24 to open movable housing 23 at a given angle, and stopping a force in the open direction of folding mechanism 10 by means of the stopper mechanism between stationary housing 22 and movable housing 23, a turning force of movable body 4 biased by spring 6 transmits to stationary housing 22 and movable housing 23 as an impact. Consequently, a loose grasp of the electronic device may cause the device to fall off the hand due to this impact. In order to prevent this problem, a damper mechanism made of an elastic body such as rubber needs to be provided separately between stationary housing 22 and movable housing 23, resulting in a complicated structure of the device.